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Originally published January 10, 2010 at 8:08 PM | Page modified January 10, 2010 at 11:48 PM

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Cutting headlight glare on I-405 through Renton

The state Department of Transportation plans to install taller median barriers to help cut oncoming headlight glare on Interstate 405 through the Renton area, and it explains why loud pavement grooves are necessary in some areas.

Seattle Times staff reporter

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Q: Drivers cheered a few years back when "glare screens" started showing up, mounted atop the median barrier between eastbound and westbound lanes along Highway 520 in the Medina area, just east of Lake Washington.

Many agreed the screens — they look somewhat like green fencing — helped to cut the glare of headlights of oncoming traffic and improve visibility during hours of darkness. Because the 520 corridor is so narrow — two main lanes in each direction — drivers had complained that headlight glare was a real safety hazard.

Bellevue resident Joe Rodriguez says Interstate 405 through the Renton area should also be a candidate for glare screens. He says he finds himself blinded by the bright lights of oncoming traffic.

"The lights are especially problematic in the rain," he said. Thus his question: Has the state Department of Transportation considered installing the same light barriers on that stretch of I-405?

"It seems it would make for a much safer ride," he said.

A: The simple answer is yes and no. The state Department of Transportation (DOT) won't be installing glare screens on Highway 405 like those on Highway 520, but the department does plan to install median barriers taller than the existing ones, and that should help cut the oncoming traffic glare, said Steve Peer, a DOT spokesman.

Bronlea Mishler of the DOT says the new barriers will be 42 inches high — a foot higher than existing ones.

The state says the Highway 520 glare screen was the best solution at the time for that stretch of roadway because of the closeness of the opposing lanes in each direction and the lack of an inside roadway shoulder. The 42-inch barrier, while more costly, is considered safer in collisions than a 30-inch barrier with a glare screen on top, says Peer.

The taller barriers already are in place on some parts of I-405 between Interstate 5 near Southcenter and Highway 167 in the Renton area, and along Highway 167 between Renton and Auburn.

Mishler says the state will also be installing the taller barriers along most of I-405 between Highways 167 and 169 in the Renton area, as part of a project scheduled to be completed in the spring of next year.

The state also has drawn up plans for taller barriers along I-405 north of Highway 169 into the Bellevue area. But as almost everyone knows, money is tight these days. "We are currently pursuing funding options for construction," Mishler said.

State officials say there's a master plan to eventually upgrade the entire I-405 corridor with 42-inch-high barriers, from Southcenter to Lynnwood.

Q: John Dewhirst, of Edmonds, says he and his wife rumbled, without warning, across rows of parallel grooves ground into the pavement in the right lane on sections of Interstate 90 between Snoqualmie Pass and Ellensburg and also on Interstate 5 between Burlington and Bellingham not so long ago.

"These grooves significantly increase the road noise while riding in both our car and van to the point that both my wife and I start driving in the left lane, which is not a good practice, for some quiet," he said.

"Could you ask around why these grooves are necessary?"

A: State transportation officials say that's a frequently asked question. The grooves are where there's a "dowel bar retrofit" — steel bars in the concrete to help hold concrete panels together.

The DOT's Bronlea Mishler says the dowel bars were installed after the pavement started showing signs of rough edges and gaps between concrete panels, caused by heavy use and deterioration in the right lanes of those roadways.

The process of installing the steel bars is called dowel-bar retrofitting. Slots are cut in the pavement where two panels join and a dowel bar is placed in each slot to secure the panels. Then the slots are filled with concrete.

Mishler says retrofitting restores the structural integrity of the roadway and extends the life of the pavement.

Dowel-bar retrofits can be found in a number places along roadways across the state, including southbound Interstate 405 south of downtown Bellevue.

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